In a drip irrigation system a liquid, such as water and/or a fertilizer or other additive, is delivered directly to each plant in an orchard, vineyard, or other agricultural system in very small, controlled quantities. A number of patents describe emitters designed for drip irrigation systems of this type, such as U.S. Pat. Nos. 3,791,587; 3,546,884; 3,807,430; 3,833,019; and 3,767,124.
Almost all emitters are designed to deliver liquid at relatively low flow rates. For example, a flow rate of approximately one gallon per hour might be desired. A difficulty which arises with many emitter designs is that in decreasing the flow orifice size of the emitter to the degree necessary to achieve the desired low flow rate the emitter becomes increasingly susceptible to clogging by dirt or other foreign particles.
While many drip irrigation systems attempt to combat this problem by periodic back flushing of the system, U.S. Pat. No. 3,780,946 describes an emitter which consists of at least two resilient diaphragms having orifices formed therethrough so that during normal operation the pressure drop across each orifice is equal to the total pressure drop across the entire emitter divided by the number of orifices, but when an orifice becomes clogged, the total pressure drop for the emitter takes place at the clogged orifice, thereby exerting sufficient pressure against the diaphragm in which the clogged orifice is formed to expand the diameter of the orifice and allow the clogging particle to pass through.
With the construction described above although a self-purging action may be attained, it will be apparent that if there are fluctuations in the inlet pressure to the emitter there will be corresponding fluctuations in the flow rate through the emitter. In fact the resilient characteristic of the diaphragms may accentuate these changes, since an increase in inlet pressure will tend to increase the area of the orifices through the diaphragms and increase the rate of flow through the emitter.